1. Field of the Disclosure
The described technology relates to a fuel cell stack. More particularly, it relates to a structure of a separator of a fuel cell stack.
2. Description of the Related Technology
A fuel cell system includes a fuel cell stack generating electrical energy by an electrochemical reaction between a fuel (hydrocarbon fuel, pure hydrogen or reformed gas rich in hydrogen) and an oxidant (air or pure oxygen). A direct oxidation fuel cell uses a liquid or gaseous hydrocarbon fuel. A polymer electrode fuel cell uses pure hydrogen or a hydrogen-rich reformed gas as a fuel.
A membrane-electrode assembly generally includes an electrolyte membrane, an anode formed on one surface of the electrolyte membrane and a cathode formed on the other surface of the electrolyte membrane. A first separator positioned on the anode side of the membrane electrode assembly has a fuel channel formed on a surface facing the anode. A second separator positioned on the cathode side of the membrane electrode assembly has an oxidant channel formed on a surface facing the cathode. Two fuel manifolds and two oxidant manifolds are formed on the corners of each separator. The fuel channel is connected to the two fuel manifolds and the oxidant channel is connected to the two oxidant manifolds.
The fuel channel and the oxidant channel include recessed grooves having a cross-sectional area much smaller than that of the fuel manifolds and the oxidant manifolds. Accordingly, when a fuel enters the fuel channel from the fuel manifolds and an oxidant enters the oxidant channel from the oxidant manifolds, the flow path (of the fuel or the oxidant, respectively) is abruptly narrowed such that a flow rate and a pressure rise.
High fluid pressure causes stress on the system concentrated in an area of the anode into which the fuel is introduced and also in an area of the cathode into which the oxidant is introduced. Moreover, the high fluid pressure at the entrance of the fuel channel and the entrance of the oxidant channel makes it difficult to uniformly distribute the fuel and the oxidant along the fuel channel and the oxidant channel.
Further, since the oxidant supplied to the fuel cell stack is not humidified, the area of the cathode into which the oxidant is first introduced operates in a very dry state. This gives rise to a condition in which radicals (produced during the operation of a membrane-electrode assembly) exist within the membrane-electrode assembly for unusually long periods of time. The increased number of radicals results in deterioration of the membrane-electrode assembly.